A diagnosis regarding the presence of a lesion or the kind of a lesion by observing a tissue section obtained from a human or an animal with a microscope, so called a pathological diagnosis, has been actively performed. In pathological diagnosis, first, a sampled tissue is dehydrated and blocked with paraffin to fix the tissue and cut into sections having a thickness of 2 to 8 μm, the paraffin is removed therefrom, and the sections are stained. Subsequently, an image data (a morphological image) is generated by microscopic observation. Diagnosis on the basis of the image data is performed by analyzing the changes in size and shape of a cell nucleus, morphological information such as change in tissue pattern, and staining information. It takes a lot of time and causes error for each operator to manually extract the region of observation target, such as a cell nucleus, from the morphological image. Recently, many techniques have been suggested for automatic image analysis in order to efficiently grasp a cancer region in which specific protein excessively express from the entire image of tissue section.
For example, according to the technique described in Patent Document 1, a cell nucleus region is extracted from an image, and a cell region is estimated as a circular region including a region expressing a specific protein on a cell membrane and having a predetermined radius from the center of gravity of the cell nucleus region.
The area and shape of one cell region in a tissue section can be different in morphological image according to the position to cut cells. For example, when the cells having the same size and the same shape arranged are cut by the cross section Z as in the schematic diagram in FIG. 22A, the area of cell regions are largely different from cells to cells as in FIG. 22B, which is a schematic morphological image captured from the direction orthogonal to the cross section Z. The biological substances expressed on a cell membrane are observed near the contour of each cell region as shown by ● (black circle) in FIG. 22B.
While the amount of biological substances is desired to be normalized on the basis of cell area and perimeter observed in morphological images, a cell region is determined as a circular region having a certain area according to the technique described in patent document 1. Such circular region is largely different from the actual cell region observed in the morphological image, and is not suitable for normalization on the basis of cell area.
According to the technique described in Patent Document 2, the position of cell membrane is specified on the basis of the light emission from the fluorescent substance which is used for staining cell membrane. The area and perimeter of cells can be calculated by the method in Patent Document 2.